Various propulsion systems have been proposed for water-going vessels in which one or more propellers are disposed below the waterline of the vessel for surface vessels or disposed within a portion of the hull of submersible vessels. Typically, the propellers in submersible systems have been driven by diesel power, steam turbines or electric motors mounted within the hull of a vessel. A propeller shaft extends through the hull to the propeller mounted on the shaft outside the hull. Such systems have the disadvantages of shaft vibration and noise radiating from the shaft. Further, leaking around the shaft occurs when the seal becomes loose or worn. Alternative systems have been suggested using shaftless electric motors mounted outside of the hull with only electric power cables passing through the hull, as shown for instance in U.S. Pat. No. 3,182,623. A disadvantage of such a system is that propulsors (electric motors and impellers) occupy almost the entire interior of the tail section. Additionally, traditional shaftless electric motors are either too small to effectively move a vessel or, if large enough, add significant weight to the vessel.
An improved marine propulsor has been disclosed in U.S. Pat. No. 5,078,628, incorporated herein by reference. The propulsor comprises a shaftless electric motor with disk-shaped rotor and stators mounted in the vessel structure with a blade assembly mounted on the rotor. The blade assembly includes a blade hub and propeller blades extending beyond the circumference of the vessel housing. An improved bearing assembly for this propulsor has been disclosed in U.S. Pat. No. 5,286,116, also incorporated herein by reference. This bearing assembly comprises a bearing support, bearing cones circumferentially mounted on the bearing support and a rotating bearing member. The bearing assembly permits water to be introduced into the system through an opening in the bearing support and a gap between the bearing cones. The water supplied by this system cools the rotor and stators of the motor as well as the bearing members. The water also lubricates the rotating components. Thus, the water acting as both coolant and lubricant prevents overheating and excessive wear due to friction.
The pumping forces generated by the rotation of the rotor cause the water to flow through the propulsor. The water in this bearing assembly exits through the gap between the blade hub and the vehicle body on both sides of the hub. This water exiting at the inlet and outlet of the propulsor blades has been found to decrease the efficiency of the propulsor.
Accordingly, the object of the present invention is to provide an improved cooling and lubricating system for a marine propulsor which does not compromise the efficiency of the propulsor, and in which the coolant/lubricant is discharged on the trailing edge of the blade assembly. Other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.